be removed by other means and a separation is thus effected by the first principle enunciated at the beginning of this section.
The knowledge of the resistance offered by a viscous fluid to the passage of a solid body through it, is far from being perfect. At high velocities, since there is a continu-
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.Hindered Settling Ratios* PIG. 1.
ous pushing aside of the fluid by a mass of cross-section A and with a velocity V it would be expected that the energy consumed would be all or a portion of the energy given out by a flowing stream of cross-section A and velocity V. In addition to this there would be a force required to overcome the viscosity of the fluid, and since the surface of the grain and the velocity with which it is moving are the origin of this viscosity, it would be expected that it would be proportional to both of these factors.
FIG. 2.—Theoretical settling in jigging.
Now at high velocity the retardation produced by viscosity is so small a portion of the total impedence that it can be neglected, and only the pressure produced by the moving grain need be considered. This is found to vary with the shape of the grain; for example, a smooth shuttle shaped grain, moving downward with its long axis parallel to the direction of motion offers no resistance or practically no resistance to the fluid, for the anterior pressure created by the down movement is balanced by a minus posterior pressure, and there exists no tendency whatever to set the fluid outside of such a body in motion. If, however, a flat grain be falling in a fluid, and